[WIP] Praga Trial Truck 6x6

[TexasEngineer454]

This turned out awesome! Great build!

This build inspired me to start my own 6x6 RC vehicle and I had a few questions for you.

What is the gear ratio coming from your drive motor? 

Any issue with not using differentials on the axles? 

[2GodBDGlory]

Nice pictures! Did you change anything since our race?

[Teo LEGO Technic]

13 hours ago, TexasEngineer454 said:

This turned out awesome! Great build!

Thanks a lot!! 

To answer your questions:

The gear ratio coming out of the gearbox is:

1. Low gear: 1:1.4
2. High gear: 1:3.89

The gear ratio from the gearbox output to the wheel, in the transmission, is 12.58:1, so the final ratios are:

1. Low gear: 8.99:1
2. High gear: 3.23:1

As for the lack of diffs, I did not find this to be an issue. My steering axle had a sharp steering angle, which allowed the truck to have a good turning radius despite not having diffs to allow the wheels to turn at different speeds in corners. While the turning radius would have been improved slightly with open/lockable diffs, I think it was a good call because it saved weight by eliminating a diff locking mechanism. As well, the combination of planetary hub + defender rims made the pivot very close to the center of the wheel, which reduced the strength needed to steer.

12 hours ago, 2GodBDGlory said:

Nice pictures! Did you change anything since our race?

Thanks! The only mechanical change is I added a stopper on the middle axle so that the drive axle doesn't slip out under any circumstances. Other than that, the only change is to the look of the cabin

[Teo LEGO Technic]

On 9/27/2023 at 6:49 PM, 2GodBDGlory said:

Nice pictures! Did you change anything since our race?

Thanks! The only mechanical change is I added a stopper on the middle axle so that the drive axle doesn't slip out under any circumstances. Other than that, the only change is to the look of the cabin

Update October 3rd

The video is completed, here it is! 

 

 

Edited October 3, 2023 by Teo LEGO Technic

[1gor]

Is it podsible to see how it looks Unimog Tire with Defender wheel and dish 6 x 6 as cover?

Off road capability is great IMHO

[Zerobricks]

It came out really great! Congratulations, hope to see it in real lifr one day, Also I see you flipped the tyres, is there any difference in performance?

[gyenesvi]

Now that's some nice off-road performance, and also good speed in high gear! It's great to watch that suspension at work.

On 9/27/2023 at 11:28 PM, TexasEngineer454 said:

Any issue with not using differentials on the axles? 

Actually, those axles would have issues if there would be differentials in there :) Those axles are from @Attika, and he had the so called quarter stud problem in the original version, which were built with diffs; in short, it would require to have lego axles that are about a quarter stud longer because of the downward angling of the driveshaft coming out of the diffs. With axles of regular length, they can slide out of the differential under torque, because the diff only holds them on half stud length, and so if there's quarter stud movement allowed, it can disengage. So this is solid exactly because it does not have a diff, and so the axle in the middle is a single piece connecting both sides, so it cannot slide out of the diff.

On 9/28/2023 at 1:28 PM, Teo LEGO Technic said:

As well, the combination of planetary hub + defender rims made the pivot very close to the center of the wheel, which reduced the strength needed to steer.

And I think this helps a lot to make it good enough without diffs, because this way the wheels don't go in opposite directions when steered (as would be the case with a high scrub radius steering). So all in all, it's a nice combination.

[Teo LEGO Technic]

1 hour ago, gyenesvi said:

With axles of regular length, they can slide out of the differential under torque, because the diff only holds them on half stud length, and so if there's quarter stud movement allowed, it can disengage.

Good point, that's definitely the case. I was thinking about the question of diffs vs. no diffs more generally, not for this specific axle. 

Edited October 3, 2023 by Teo LEGO Technic